Electronic apparatus for accurately monitoring and recording the partial pressure of a gas

ABSTRACT

An electronic apparatus for continuously metering and recording the partial pressure of CO2 including a voltage sensitive meter and recorder. The meter is adapted to receive and read voltage generated by an electrode representative of the partial pressure of CO2 in a stream of liquid introduced to the electrode. The recorder is adapted to record the voltage output from the meter together with a compensating voltage or in the alternative to record a pre-determined voltage which may be set independently of the voltage output of the meter. Electronic circuitry allows the recorder to automatically monitor the electrode voltage together with a compensating voltage. The circuitry also allows the periodic recalibration of the voltage supplied to the recorder. The calibration and monitoring of the partial pressure of CO2 may be done either manually or automatically. The electronic circuitry generally includes resistive networks, power supplies, time delay units, solenoid coils and associated relays.

nited States Patent McFarland et al.

[4 1 July 18, 1972 Otho K. McFarland, Gl'encoe; James F. Tamburrino,Chicago, both of Ill.

Abbott Laboratories Sept. 24, 1969 Inventors:

Assignee:

Filed:

Appl. No.:

US. Cl. ..324/29, 204/195 P, 324/30 R Int. Cl. ..G0ln 27/42 Field ofSearch ..324/30, I30, 29; 204/195 P;

23/232 E, 254 E, 255 E References Cited UNITED STATES PATENTS 6/1957Jacobson ..324/30 Primary ExaminerMichael J. Lynch Attorney-Molinare,Allegretti, Newitt & Witcoff ABSTRACT An electronic apparatus forcontinuously metering and recording the partial pressure of CO,including a voltage sensitive meter and recorder. The meter is adaptedto receive and read voltage generated by an electrode representative ofthe partial pressure of CO in a stream of liquid introduced to theelectrode. The recorder is adapted to record the voltage output from themeter together with a compensating voltage or in the alternative torecord a pre-determined voltage which may be set independently of thevoltage output of the meter. Electronic circuitry allows the recorder toautomatically monitor the electrode voltage together with a compensatingvoltage. The circuitry also allows the periodic recalibration of thevoltage supplied to the recorder. The calibration and monitoring of thepartial pressure of CO may be done either manually or automatically. Theelectronic circuitry generally includes re sistive networks, powersupplies, time delay units, solenoid coils and associated relays.

5 Clairm, 4 Drawing figures 56 52 V i r 3 (3 T 54 46 l J 60 6L0 -64 62 ii E j, 7? STANDARD 6A5 v 66 58 I /08 PNEUMAT/C All? PATENTEU JUL 1 8I972 SHEET 2 BF 2 FROM ELECT aurpur ELECTRONIC APPARATUS FOR ACCURATELYMONITORING AND RECORDING THE PARTIAL PRESSURE OF A GAS BACKGROUND OF THEINVENTION The electronic apparatus of applicants invention has beenconstructed in order to provide a method for automatically standardizingand calibrating a sampling apparatus for monitoring the partial pressureof a gas. In a particular application, this circuitry was designed foruse with an electrode for generating a voltage representative of thepartial pressure of CO in a liquid solution. However, according to theprincipals of applicants invention, the circuitry disclosed would beeasily employable for use with a standard electrode. For example, thiscircuitry could be applied in an electrode which generates a voltagerepresentative of the concentration of hydrogen ions in a particularsolution.

The electronic apparatus constructed in accordance with the principalsof ,our invention provides means for continuously metering and recordingthe output of a sensing electrode accurately and efficiently. Theelectronic apparatus of our in vention automatically standardizes andrecalibrates the recorder at predetermined intervals. The electronicapparatus of our invention provide manually operable controls forstandardizing and recalibrating the recorder at any desired time.Accordingly, the electronic apparatus of our invention substantiallyreduces the possibility of error in the readout of the electrode outputby periodically recalibrating the recorder reading. The electroniccircuitry of our invention also provides a recording of the errorvoltage from the electrode dur ing the calibration of the recorder.

SUMMARY OF THE INVENTION In one principal aspect, an electronicapparatus is provided for use with an ion sensing electrode comprisingthe combination of a readout device for recording a voltage impressedthereon having a voltage input terminal, means for automati callyimpressing a predetermined voltage representative of ion concentrationof a standard solution on the input terminal, means for automaticallystoring a compensating voltage representative of the difference betweenthe predetermined voltage and a voltage generated by the sensingelectrode representative of the ion concentration of the standardsolution, and means for automatically impressing the compensatingvoltage across the input in series with a sample voltage generated bythe sensing electrode representative of the ion concentration of asample solution such that the compensating voltage and the samplevoltage in series are more truly representative of the ion concentrationof the sample solution than is the sample voltage alone.

In another principal aspect, an improvement in electronic apparatus forcontinuously recording the voltage output of a sensing electroderepresentative of the partial pressure of a gas in a liquid solution isprovided. The electronic apparatus for recording a voltage has a voltageinput terminal, a moveable sheet for recording thereon, and a recorderpen responsive to the voltage impressed on the input terminal. Theimprovement comprises means for automatically impressing a predeterminedvoltage representative of the partial pressure of a standardized gas onthe input terminal, means for automatically storing a compensatingvoltage representative of the difference between the predeterminedvoltage and the voltage generated by the electrode means representativeof the partial pressure of the standardized gas, and means forautomatically impressing the compensating voltage across the input inseries with a sample voltage generated by the electrode representativeof the partial pressure of a gas in sample liquid solution such that thecompensating voltage and the sample voltage in series are more trulyrepresentative of the partial pressure of the gas in the sample liquidsolution than is the sample voltage alone.

In still another principal aspect, an improvement in an electronicapparatus for continuously monitoring the voltage output of a sensingelectrode representative of the partial pressure of a sample gas in aliquid solution having a voltage input terminal and recorder means forresponding to the voltage impressed on the input terminal. Theimprovement comprises automatic switching means for impressing acompensating voltage across the input terminal in series with the samplevoltage generated by the electrode when the sample solution isintroduced to the input of the electrode, sample measuring timer meansfor breaking a contact after a predetermined sample measuring time,electrode input solenoid means responsive to the breaking of the contactfor alternating the input of the electrode from the sample solution to astandarized gas the partial pressure of which is known, standardmeasuring timer means responsive to the breaking of the contact forbreaking a second contact after a second predetermined time after thebreaking of the first contact, calibration means responsive to thebreaking of the second contact for switching the input of the recorderfrom the electrode voltage output to a predetermined voltagerepresentative of the partial pressure of the standardized gas, meansresponsive to the breaking of the second contact for deactivating theelectrode input solenoid after a third predetermined time after thebreaking of the second contact such that the electrode input isalternated from the standardized gas to the sample solution, meansresponsive to the breaking of the second contact for switching the inputof the recorder from the predetermined voltage to the electrode voltageand the compensating voltage in series, and means responsive to thebreaking of the second contact for actuating the sample measuring timermeans.

BRIEF DESCRIPTION OF THE DRAWINGS In the course of this description,reference will frequently be made to the attached drawings in which:

FIG. 1 is an elevation partial cross-sectioned view of a preferredembodiment of gas partial pressure sampling as sembly.

FIG. 2 is an enlarged partially cross-sectioned view of the sensingelectrode of the sampling assembly.

FIG. 3 is a schematic presentation of operation of the sensing electrodeof the sampling assembly.

FIG. 4 is a circuit diagram showing the preferred embodiment of theelectronic apparatus of our invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The Sampling Assembly A In FIG.1, a preferred embodiment of the overall sampling assembly is shownwhich includes a housing block 10, formed of a suitable transparentmaterial such as lucite. The block 10 has a plurality of major bores l2,l3 and 14 formed therein which extend from the exterior of the block andmeet at one end to form a sampling chamber or cavity 16. An ionsensitive pH electrode, generally 18, is positioned in bore 12 andprovided with suitable O-rings 20 to prevent leakage past the electrodefrom the cavity 16 to the exterior of the block. The specific details,principles of operation and modifications of the electrode will beoutlined in more detail later.

Positioned in bore 13 is a nebulizer, generally 22, for calibrating theelectrode periodically during operation. The nebulizer 22 includes atubular neck 24 which communicates with a chamber 26 and an O-ring 28 isprovided about the sampling cavity end of the neck 28 to prevent leakagefrom the cavity ,16 between the neck and the bore 13. The neckcommunicates with terminates in the enlarged bulbous nebulizing chamber26, a portion of the chamber being positioned beneath the neck so as toprovide a sump 30 for holding a portion of liquid when the cavity 16 isdrained. A liquid aspiration conduit 32 communicates at one end with thesump 30 and the other discharge end is positioned adjacent the dischargeend of a gas inlet conduit 34 which is connected to a supply of standardcarbon dioxide gas. A spray diffuser 35 is also positioned adjacent thedischarge ends of conduits 32 and 34 to assist in forming a uniformvapor atmosphere during the calibration operation which will bedescribed in more detail later. Positioned in the upper portion of thechamber 26 is an overflow discharge outlet 36 which communicates with adrain conduit 38 connected at the other end to a waste manifold 40. Thedischarge outlet 36 is positioned at the top of the chamber so as tomaintain the sample cavity 16, tubular neck 24 and a major portion ofthe nebulizer chamber 26 continuously full of the liquid being sampledduring the monitoring operation.

A small bore impinger 42 is positioned in a bore 44 of block andcommunicates at one end with a sample inlet conduit 46 which isconnected to a production flow line or the like L and a suitablecontinuously operating constant delivery peristaltic pump 47 continuallydiverts and delivers a small continuous portion of flow from flow line Lto the impinger for injection into the cavity 16. The other end of theimpinger 42 is positioned closely adjacent a membrane 48 which coversthe end of the electrode 18 such that the fluid stream issuing from theend of the impinger 42 gently plays upon the membrane.

A bypass bore 50 is provided in the housing for diverting the sampleinlet stream from the impinger 42 to the waste manifold 40 through adrain conduit 54 and a bypass valve 52, which is preferablypneumatically actuated. A drain valve 56, which is also pneumaticallyactuated, is also provided which communicates with bore 14 for drainingthe cavity 16 through the drain conduit 54 to manifold 40.

A carbon dioxide standard gas piping arrangement is provided whichincludes a main conduit 58 which is adapted to be connected to a sourceof standard carbon dioxide gas at a given pressure. A branch conduit 60connects the main 58 with the gas inlet conduit 34 to the nebulizer 22through gas line 61. A small orifice 62 is provided in the branch 60 tomaintain a small flow of standard gas to the nebulizer at all timesduring the monitoring cycle. Such flow maintains the liquid whichsubstantially fills the nebulizer chamber 26 in a slightly agitatedstate and prevents clogging of the relatively small discharge aperturesin the ends of conduits 32 and 34 and the accumulation of stale liquidin sump 30. A second branch conduit 64 extends from the main 58 througha pneumatically actuated valve 66 and is connected to the gas line 61 inbypassing relationship to the orifice 62 for introducing the standardcarbon dioxide at an increased flow rate to the nebulizer during thecalibration stage which will be described in more detail later. A thirdconduit 68 extends from the main 58 to a relatively small injection bore70 for feeding the standard carbon dioxide gas to the electrode 18, theconstruction and purpose of which will be described in more detaillater. The flow through conduit 68 is metered by a metering valve 72.

The Electrode Referring to FIGS. 2 and 3, the electrode 18 is a pH glasselectrode which is constructed to signal the pH of a thin film ofaqueous sodium bicarbonate buffer solution. The electrode includes agenerally cylindrical elongated tubular glass element 74 which issurrounded by a tubular concentric jacket 76 which is formed ofstainless steel or other suitable strong material and which forms ahousing for the electrode. The inner diameter of the jacket 76 issomewhat greater than the diameter of the glass element 74 so as toprovide an annular recess 78 which acts as a reservoir of sodiumbicarbonate buffer solution. Still another elongated tubular cylindricalglass element 80 is concentrically positioned within element 74 and issealed therefrom, the space between the outer wall of element 80 and theinner wall of element 74 forming a first annular reference electrodechamber 82 and the interior of element 80 defines a second sensingelectrode chamber 84. Each ofthe chambers 82 and 84 is filled with a KClelectrolyte solution of approximately 0.1 M, and a mercury amalgamreference electrode 86, such as a calomel electrode is positioned in theelectrolyte in chamber 82 and a calomel sensing electrode 88 ispositioned in the electrolyte in the sensing chamber 84.

The end ofelement extends beyond element 74 at 89 and an O-ring 90 ispositioned about the extended end to form an operating chamber 92 at theextended end 89 and separates the chamber 92 from the buffer solutionreservoir 78. The open of the jacket 76 is covered with the membrane 48,the membrane being permeable to the gas which is to be measured, in thisinstance carbon dioxide. The membrane is preferably formed of a thinTeflon film which allows the passage of carbon dioxide, but whichprevents the passage of any other molecules which might adverselyalterthe pH of the buffer solution. The membrane 48 is sealingly secured by asuitable means to the end of the jacket 76. such as by an elastic band94 which cooperates with an annular notch 96 in the end of the jacket. Athin layer of nylon mesh or grid 98 is packed between the membrane 48and the tip of the extended glass sensing element 89 and the mesh issaturated with the sodium bicarbonate buffer solution. The O-ring 90substantially seals the operating chamber 92 from the bicarbonate bufferreservoir 78, but allows a slight transfer of the buffer solution backand forth to maintain the buffer in the operating chamber in areplenished and steady state.

An O-ring 100 is provided at the other enlarged end of glass element 74to prevent leakage from the reservoir 78 to the exterior of theelectrode. A cap member 102 is fitted over the end of thejacket and themembrane 48 is exposed through an aperture 104 in the cap.

The electrode thus far described is basically a Severinghaus CO cellwhich is obtainable from Instrumentation Laboratories, Boston,Massachusetts. Severinghaus electrodes have been used in the pastprimarily for batch pH measurements and are generally unacceptable assuch for the continuous online monitor which is contemplated by ourinvention, due to rapid and excessive drift. Such drift apparentlyresults from a migration of bicarbonate ions between the operatingchamber 92 and the reservoir 78 and since the diffusion rate past theO-ring 90 never reaches a steady state, a long-term drift in electrodepotential results. It has been found that this drift in the Severinghauselectrode can be prevented by continuously bleeding a small amount ofgas ofa fixed carbon dioxide content into the reservoir 78. The presenceof the gas in the reservoir tends to stabilize the carbon dioxidepartial pressure in the buffer solution and maintains a steady stagediffusion between the operating chamber 92 of the electrode andreservoir. The bleed rate may be adjusted by the metering valve 72.

Description of Operation of the Sampling Assembly During Monitoring Atthe commencement of monitoring of the intravenous solution bypass valve52, drain valve 56, and nebulizer gas valve 66 are closed and a smallportion of the production liquid intravenous stream is continuouslydiverted from the production flow line L by pump 47 and passes throughthe sample inlet conduit 46, through bore 44 and through the impinger42, discharging against the sampling cavity side of the Teflon membrane48 of the electrode 18. The carbon dioxide, the partial pressure ofwhich is to be measured, has been previously mixed into the intravenousliquid passing through line L. Therefore, the sample portion which isdiverted from line L and passed to the sampling cavity is ofsubstantially the same gas content as the main stream.

Since the drain valve 56 is closed, the sample flowing through theimpinger 42 will collect in cavity 16 and fill the sampling cavity andthe neck 24 and a major portion of the chamber 26 of the nebulizer thelevel in the chamber 26 being fixed by overflowing at outlet 36 andpassing through drain conduit 38 to waste manifold 40.

When the cavity 16 is full, the membrane 48 is completely contacted bythe body ofliquid in the cavity and the impinger directs its stream intothe body of liquid. ln actuality, the stream flowing from the impinger42 does not actually impact the membrane 48 as such, but is injectedinto the body of liquid in such a manner that the stream reaches themembrane in a substantially non-pressurized state and continuouslysupplies the membrane with fresh sample liquid at all times displacingaway from the membrane 48 the fluid which has just previously beenmonitored. The discharge rate of the impinger 42 and the distancebetween the impinger tip and the membrane should be adjusted such thatthe stream issuing from the tip of the impinger into the body of liquidjust falls short of pressurized impact on a membrane since increasedimpact pressure on the membrane will result in increased diffusion ofcarbon dioxide across the membrane and provide erroneous partialpressure readings as will become evident when considering thedescription of the electrode operation which will be described in moredetail later. The flow rate and impingerto-membrane distance may bereadily determined by one of ordinary skill in the art when he considersthe requirement of avoiding pressurized impact. Since the impinger 42continu ously supplies the membrane 48 with fresh sample intravenoussolution and sweeps away liquid from the surface of the membrane whichhas already been analyzed, and since the cavity 16 is maintainedcompletely filled at all times during the measuring operation, thelikelihood of erroneous readings due to the presence of gas bubbles andstale liquid is substantially reduced, if not eliminated altogether,such being a necessity in the continuous monitoring operationcontemplated.

Referring particularly to FIGS. 2 and 3, as the intravenous liquid withthe inert carbon dioxide gas suspended therein contacts the Teflonmembrane 48, a certain amount of the carbon dioxide diffuses through themembrane either from or to the operating chamber 92 and the sodiumbicarbonate buffer solution contained therein. The amount of carbondioxide which diffuses through the membrane will depend upon thebicarbonate ion concentration in the buffer solution and the amount, andhence the partial pressure, of carbon dioxide which is carried by theintravenous solution. For a given buffer concentration if the partialpressure of the carbon dioxide is relatively high, carbon dioxide willtend to diffuse through the membrane from the cavity 16 to the buffersolution. Such addition of carbon dioxide will drive the ion equilibriumequation in one direction such that the H* ion concentration in thesensing chamber will increase. Since the tip of the glass element 89 ispermeable to H ions, the increase in H ion concentration will tend tocause H ions to diffuse from the solution in chamber 92 to theelectrolyte in the sensing electrode chamber 84 to change the potentialof the cell in the manner comparable to a conventional standard pHelectrode. 0n the other hand, if the partial pressure of the carbondioxide in the cavity is low, carbon dioxide will tend to diffusethrough the membrane from the buffer solution to the cavity 16 drivingthe equilibrium equation in the opposite direction, reducing the l-l ionconcentration in the buffer solution and effecting a diffusion of H ionsfrom the electrolyte to the buffer solution.

The nylon mesh 98 tends to maintain the buffer solution in continuouscontact with both the tip 89 of the extended end of the glass electrodeand the Teflon membrane 48 and allows steady state equilibrium to beattained more rapidly. The mesh is maintained in a saturated conditionby the reservoir 78 to bicarbonate solution and acts as a salt junctionbetween the measuring tip 89 and the reference electrode 86 via a tinyaperture 106 in element 74 which communicated between reservoir 78 andthe reference electrode chamber 82.

The buffer solution is preferably selected to be of a concentration suchthat the electrical output of the electrode is approximately 56millivolts for each lO-fold change in the partial pressure of the carbondioxide. A suitable buffer solution may be obtained from InstrumentationLaboratory, Inc., Boston, Mass. as their solution No. 106-22. When suchsolution is used, the pH of the buffer solution has been found to fallabout 1 pH unit for each ten-fold increase in pCO Thus providing a Phvariation which is a linearfunction of the logarithm of CO During themeasuring cycle of the monitor, a standard carbondioxide gas iscontinuously fed through metering valve 72 to reservoir 78 and also fedthrough the orifice 62 to the gas inlet conduit 34 of the nebulizer 22for the reasons previously described. The flow to the reservoir 78 isonly slight and is just enough to maintain the buffer saturated withoutpressurizing the reservoir to any appreciable extent. The flow throughthe tip of the inlet 34 is also small and no atomization if fluid occurssince the nebulizer chamber 26 is maintained substantially filled at alltimes during the monitoring operation.

Description of Operation of the Sampling Assembly During CalibrationAlthough the bleed of carbon dioxide into reservoir 78 substantiallyreduces drift in the electrode, some drift will occur over an extendedtime. For this reason the readout circuit should be periodicallyrecalibrated to prevent erroneous readings caused by long term drift. Asuitable control valve 108 is opened periodically to introduce workingair to valves 52, 56 and 66 to open the valves simultaneously. Openingof valve 108 may be automatically controlled by a timer if desired. Whendrain valve 56 is opened, the liquid which fills the cavity 16 and thenebulizer chamber 26 is drained to the drain conduit 54 and into wastemanifold 40, with the exception of a small portion of the liquidremaining in the sump 30 in nebulizer chamber, the level being shown bythe dotted line in FIG. 1. The opening of the bypass valve 52 divertsthe sample stream from the impinger 42 to the drain conduit 54 and thewaste mainfold and the sample stream thereby ceases to issue into thecavity 16 from the impinger. When valve 66 is opened, the standardcarbon dioxide gas bypasses the orifice 62 and is introduced directlyinto gas line 61 and flows to the nebulizer inlet conduit 34. Theincreased flow of gas across the tip of the liquid aspirator 32 reducesthe pressure at the tip drawing liquid from the sump 30 and atomizingthe liquid to produce a mixture of standard carbon dioxide and liquid inthe form of a gas equilibrated cloud. The cloud fills the nebulizerchamber 26, and the cavity 16 and is seen" by the membrane 48, aselected portion of the carbon dioxide gas in the cloud diffusingthrough the membrane to produce an electrode signal in a manner similarto that previously described. This signal may be readily compared withwhat the output signal should be for the given standard gas partialpressure and the signal may be compensated for accordingly as necessary.

The standard gas mixture should preferably have a pCO exceeding that ofthe intravenous solution which is to be monitored for optimum response,since the solution drawn from the sump will tend to contribute somewhatto the partial pressure of the cloud which is seen by the membrane and alonger equilibration time will be required for calibration. It has beenfound that a flow rate of standard carbon dioxide from the gas inlet 34of approximately 1 500 cc/min. is sufficient to produce the gas clouddesired while avoiding excessive use of the standard gas mixture and anycooling effect which might be brought about due to the expansion of thegas. A percent carbon dioxide standard gas is preferred at 21 C and [4.7psia to insure adequate aspiration of all intravenous solutions.

Although the liquid used in the formation of the calibration cloud hasbeen described as being the intravenous liquid which has been left inthe sump, water may also be nebulized for long continuous calibrationperiods without a fall off in the partial pressure of water as might beexperienced due to evaporation after a substantially lengthy calibrationstep with a salt solution or a heavy loaded intravenous solution. Theuse of water is not generally necessary however, since with theapparatus and method described, only a few minutes will usually berequired in most circumstances to reach equilibrium during calibration.

Electronic Circuitry According to the principles of applicants inventionthe partial pressure of the CO may be monitored by a meter and arecorder 122. As has been explained, the electrode 18 generates avoltage representative of the partial pressure of a gas. The meter 120is a common volt meter of the type well known in the art, such as aLeads and Northrup Model 7407 having a full scale reading at 200millivolts representing a two decade change from the sensing electrode.This meter 120 is capable of recording changes from 10 to 1,000 mm Hg pC The recorder 122 is of the type commonly known in the art, having astylus recording pen 124 responsive to the voltage impressed on theinput 125 of the recorder. The recorder sheet 126 on which the pen 124records may be driven by a two speed motor (not shown). The recorderselected for this particular embodiment was one of the type known as aLeads and Northrup Speedomax W recorder having a 100 millivolt fullscale input sensitivity. Because of the sensitivity differences betweenthe meter and the recorder, a 200 ohm precision resistor 128 wasconnected in parallel with the recorder output terminals 130. The outputof the meter is delivered to the recorder through conductor 132 by asingle pole double throw rotary switch 134 for changing the recorderscale from -100 mm Hg p CO to 100-1 ,000 mm Hg p CO This single poledouble throw rotary switch 134 allows the meter to read its normal twodecade scale and provides a manually operable method by which therecorder may register either of the two expanded scales by merelyalternating the switch 134. The recorder is provided with a recorderinput switch 136 which may be activated by a recorder solenoid 138 foralternating the input to the recorder 122. The recorder solenoid 138 isenergized by power delivered through a diode bridge 140 from a 100 voltto 24 volt transformer 142. Thus, whenever power is delivered to thetransformer 142, the solenoid 138 is energized and the recorder inputswitch 136 is depressed to make contact with immobile terminal 144. Whenno power is supplied to the transformer 142, the switch returns to itsnormal position in contact with upper immovable terminal 146.

As has been previously mentioned, there is inherent error in a readingtaken directly from the electrode 18. Thus a method of automaticallycalibrating the recorder has been devised according to the principles ofthe invention. To provide a predetermined voltage for the calibration ofthe recorder, a lO-turn 100 ohm micrometer 148 has been placed inparallel with the output resistive network 150 of a DC power supply 152of the type commonly known in the art. The power supply may take theform of a Leads and Northrup Regulated Power Supply Part No. 099012having a rating of 1.050 volts at 10 milliamps for a fixed resistiveload of 105 ohms. The 100 ohm micrometer 148 has a manually adjustablemicrodial 154 for dividing the fixed voltage across the micrometer 148and delivering a portion of the voltage through conductor 156 to thelower immovable terminal 144 of the recorder input switch 136. Thuswhenever the recorder solenoid 138 is activated, the single pole doublethrow switch 134 is in contact with the lower movable terminal 144 and apredetermined voltage set by the microdial 154 is impressed across therecorder input 125. As will be further explained, the depression of thecalibrate button 158 supplies power to the transformer 142 whichactuates solenoid 138 and causes the predetermined voltage to beimpressed across the recorder input 125.

A compensating voltage in series with the meter output from the movablearm 135 of the switch 134 may be produced by a resistive bridge network160 having power supplied to it by a solid state DC power supply 161 ofthe type commonly known in the art. The resistive bridge may be of thetype commonly called a Wheatstone bridge having an adjustablerestandardizing slide wire resistor 162 in series connection in one armof the bridge. The DC power supply should be connected to the twoterminals 164 and 166 not connected across the bridge arm 168.

The bridge arm 168 is series connected to the output of the meter 120.Thus the voltage across the bridge arm 168 causes a change in thevoltage across the recorder input 125 when the run recorder input switch136 is connected to the output of meter 120.

Description Of Operation Of The Electronic Metering And Recording SystemFor the operation of the system, control buttons with associated controllamps are provided. Thus when the off button 172 is depressed, switch174 is open and no power is served to any component in the system. Thepower which may be served to the basic components is of the typecommonly obtainable from a standard household outlet having 1 10 volt 60cycle per second current.

When the standby button 173 is depressed switch 174 closes and doublepole double throw standby switch 176 is moved into contact with upperimmovable contacts of the switch 176. The alteration of these switchescauses power to be served to the recorder 122 and the meter with therecorder input shorted out through the upper moveable contact of thedouble pole double throw switch 176, thus holding the recorder pen 124at the zero position. The recording sheet 126 may be set in motionthrough independent control of the recorder sheet motor (not shown). Thestandby switch 176 also activates the standby light 177 through lowermoveable contact of switch 176.

Depression of the standard button 178 causes the standby switch 176 toreturn to its normal position in contact with lower immovable member ofthe contact switch. It also causes the four movable contact members ofthe standard switch 180 to move out of their normal position and intocontact with the upper immovable contact members of the standard switch180.

Thus power may be served from power line 182 through immovable contact180c to standard light 184 and through immovable contact 180b to acontrol valve solenoid 186. When the control valve solenoid 186 isenergized, the control valve 108, is opened and, as has been described,working air is introduced to valves 52, 56 and 66 which cause thesubstitution of the sample liquid solution having a gas the partialpressure of which is to be determined for a standardized gas the partialpressure of which is known. Thus, with the standard button 178depressed, a standard gas is introduced to the electrode 18 and therecorder input 125, no longer shorted by standby switch 176, receivesthe meter output representative of the voltage generated by theelectrode 18. In this mode the recorder 122 and meter 120 may beobserved to follow a change in reading over a period of time ultimatelyreaching an equilibrium position.

Having reached the equilibrium position the calibrate button 158 may bedepressed. Depression of calibrate button 158 causes the movable contactmembers of standard switch 180 to return to normal position in contactwith lower immovable contact members. The depression of the calibratebutton 158 also causes the moveable members of double throw calibrateswitch 190 to be moved into contact with upper immovable contact membersof the calibrate switch 190. In the calibrate mode the control valvesolenoid 186 remains energized through standard switch immovable contactmember 180d and through immovable contact member 190a of calibrateswitch 190. Also the transformer 142 is energized by connection to powerline 182 through upper immovable member 190a of calibrate switch 190.The energizing of the transformer 142 also serves power to calibratelight 192 and activates the recorder solenoid 138 through the diodebridge 140. Thus the voltage impressed across the recorder input is apredetermined voltage from the 100 ohm micrometer 148 set by theadjustment of the microdial 154.

In practice this predetermined voltage is mathematically respresentativeof the partial pressure of the gas in the standard solution introducedto the electrode for calibration. The partial pressure of the standardgas is easily determinable because the analyzed percentage of the gas inthe standard solution used is known. Thus for example where the gas in-IOIIMG num troduced is 100 percent CO at 744 mm Hg atmospheric pressurein contact with water at room temperature, the gas would have a partialpressure of 720 mm Hg where the water vapor at 25 C would have a partialpressure of 24 mm Hg. On a zero to 100 scale representing l-log cyclefrom 100 to 1,000 mm Hg, 720 mm Hg would be approximately 85. Thus themicrodial 154 should be set to 85, causing the recorder pen 124 to bedriven at the 85 percent chart position.

The depression of the calibrate button 158 also activates a clutch 194which is mechanically linked to the recorder solenoid 138. The variableslide wire resistor 162 is clutch connected to the recorder slide wirespindle. Thus when the predetermined voltage from the 100 ohm micrometer148 is impressed across the recorder input through the recorder inputswitch 136, the slide wire is positioned by the clutch 94 to provide acompensating voltage across the bridge arm 168 of the resistive bridgenetwork 160.

During the initial standardization and calibration, this compensatingvoltage should be zero as the recorder value in the standard mode (wherea standardized gas is introduced to the electrode) is the same as therecorder value in the calibrate mode (where the recorder reads a portionof the voltage across the 100 ohm micrometer 148). Thereafter, thecompensating voltage is so adjusted tat the exact potential isintroduced into the meter output to retain the recorder pen 124 at thesame position maintained when the predetermined voltage is impressed onthe input of the recorder 122.

The depression of the measure button 196 causes the movable contacts ofcalibrate switch 190 to return to normal position in contact with thelower immovable contact members of the calibrate switch 190. Thus thecontrol valve solenoid 186 is no longer energized through the upperimmovable contact member 190a of calibrate switch 190. As has beendescribed the control valve 108 thus returns to its normal positionallowing valves 52, 56 and 66 to close simultaneously and cause theintroduction of the sample solution having a gas, the partial pressureof which is to be determined, into the electrode 18. The measure contactswitch 198 is made when the measure button 196 is depressed thusactivating the measure light 200.

In the measure mode the meter and recorder sense the output of theelectrode in response to the partial pressure of the gas in the samplesolution, The recorder however follows this voltage with thecompensating voltage produced by the bridge arm 168 of the resistivebridge network 160.

Description Of Automatic Operation Of The Meter And Recorder SystemAfter equilibrium position has been reached in the standard mode theautomatic button 202 may be depressed. Depression of the automaticbutton 202 causes the movable contact members of the standard switch 180to be depressed into their normal position in contact with lowerimmovable contact members of the switch 180. The depression of theautomatic button 202 also causes the movable contact members of theautomatic switch 204 to move into contact with upper immovable contactmembers of the switch 204.

The depression of the automatic button 202 activates a time delay relay206 capable of generating a wave for a predetermined time adjustablefrom zero to 30 seconds. This delayed timer may take the form of a solidstate electronic switching device Guardian type TDO-62C3-l l5A. Forexample the delay timer may generate a square wave pulse for a durationequal to the predetermined time set on the delay timer relay 206. DuringThis predetermined time the control valve solenoid 186 remains open forcalibration and the power delivered by the time delay relay 206activates the transformer 142 for switching the recorder input switch136 to the lower immovable terminal 144, thus impressing thepredetermined voltage from the 100 ohm micrometer 148 into the recorderinput. An indication may thus be made of the calibration on the chartand the standardizing timer 208 may initiate its timing cycle.

The standardizing timer 208 may take the form of a fixed speed motor(not shown) drivingly connected to a disc 210. A switch lever 212 rideson the surface of the rotating disc 210 and causes the switch 214,normally in the made position, to break contact when the switch leverrides into a depression 216 in the disc 210. Thus the contact of switch214 is broken whenever the motor (not shown) drives the disc 210 througha full revolution.

At the termination of the predetermined time duration of the pulsegenerated by the time delay timer 206, the double pole throw switch 218of the time delay timer 206 is activated and the moving members of theswitch 218 move out of normal position into contact with lower immovablemembers of the switch 218. This contact activates automatic relaysolenoids 220 and 222 causing the double pole double throw relay switch224 to be moved out of its normal position into contact with the lowerimmovable contact members of the switch 224 and causing double throwrelay switch 226 to be moved out of normal position into contact withthe lower immovable contact members of switch 226.

The switching relay switches 224 and 226 causes the deactivation oftransformer 142 and thus a return of the recorder input switch 136 toits normal position in contact with the upper immovable terminal 146 ofthe recorder input switch 136 so that the input to the recorder 122 isthe series combination of the voltage produced by the electrode 18 inseries with the bridge voltage across the bridge arm 168 of theresistive bridge network 160.

The activation of relay switches 224 and 226 also energized the sampletimer device 228. The sample timer may be a fixed slow speed motor timerof the type commonly known in the art. Associated with the sample timer228 is a solenoid 230 which is energized by the expiration of onerevolution of the sampler timer 228. The energized solenoid causes atimer switch 232 to be moved from its normal contact with the lowerimmovable terminal of the timer switch 232 into contact with the upperimmovable terminal, thus interrupting power to solenoid 220 and allowingthe return of double pole double throw relay switch 224 to its normalposition in contact with the upper immovable contacts of the switch 224.

The momentary opening of timer 232 stops the sample timer 228 andinitiates operation of the standardizing timer 208 and energizes thecontrol valve solenoid 186 which, as has been described before, causesthe replacement of the sample solution in the electrode 18 by astandardized gas. The standardizing mode into which the monitor has beenplaced is terminated by the opening of the standardizing timer switch214 as has been described. This action renews the calibration cycle byinterrupting power to automatic relay 22 which allows the switch 226 toreturn to its normal position having moveable contact members in contactwith the upper immovable contact members of the switch 226.

In its normal position switch 226 energized the time delay relay 206while permitting the control valve solenoid 186 to remain open and thestandardizing timer 208 to continue turning until the actuation of thetime delay relay switch 218 of the time delay relay 206. Finally, theactuation of the time delay relay 206 energizes automatic relays 220 and222 and deenergizes the control valve solenoid 186. The monitor is onceagain in the on-stream mode and may thus perform another complete cycle.

We claim:

1. In an electronic apparatus for use with an ion sensing electrode, thecombination of:

a readout means for recording a voltage impressed thereon having avoltage input terminal; valve control means for selectively introducingeither a standard solution or a sample solution to said electrode;

standardizing means for simultaneously operating said valve controlmeans to selectively introduce said standard solution to said electrodeand impressing an output voltage from said electrode on said inputterminal;

calibrating means for automatically impressing a pre-determined voltagerepresentative of the ion concentration of the standard solution on saidinput terminal, means responsive to said calibrating means forautomatically storing a compensating voltage representative of thedifference between said pre-determined voltage and the voltage generatedby the sensing electrode representative of the ion concentration of thestandard solution,

measuring means for selectively terminating said pre-determined voltageat said input terminal and automatically impressing said compensatingvoltage across said input terminal in series with an electrode voltagegenerated by the sensing electrode representative of the ionconcentration of a solution such that said compensating voltage and saidelectrode voltage in series are more truly representative of the ionconcentration of the solution than is the electrode voltage alone,

and means responsive to said measuring means for operating said valvecontrol means to selectively introduce only said sample solution to saidelectrode.

2. In an electronic apparatus for continuously recording the voltageoutput of a sensing electrode representative of the partial pressure ofa gas in a liquid solution having a voltage input terminal, movablesheet for recording thereon, and recorder pen responsive to a voltageimpressed on said input terminal, the improvement comprising, incombination:

valve control means for selectively introducing either a standardizedsolution or a sample solution to said electrode;

standardizing means for simultaneously operating said valve controlmeans to selectively introduce said standard solution to said electrodeand impressing an output voltage from said electrode on said inputterminal; calibrating means for automatically impressing apre-determined voltage representative of the partial pressure of the gasin said standard solution on said input terminal,

means responsive to said calibrating means for automatically storing acompensating voltage representative of the difference between saidpre-determined voltage and a voltage generated by said electroderepresentative of the partial pressure of the gas in said standardsolution,

measuring means for simultaneously terminating said predeterminedvoltage at said input terminal and automatically impressing saidcompensating voltage across said input in series with a voltagegenerated by said electrode representative of the partial pressure of agas in a liquid solution such that said compensating voltage and saidelectrode voltage in series are more truly representative of the partialpressure of the gas in said liquid solution that is the electrodevoltage alone,

and means responsive to said measuring means for operating said valvecontrol means to selectively introduce only said sample solution to saidelectrode.

3. The improvement of claim 2 wherein said calibrating means forautomatically impressing said pre-determined voltage comprise a DC powersource, a fixed impedance across said power source having an adjustablevoltage divider terminal, solenoid actuated switch means for impressinga voltage divided by said voltage divider terminal across said inputterminals of said recorder, and manually operable means for energizingsaid solenoid.

4. The improvement of claim 1 in which said means for automaticallystoring said compensating voltage comprise a resistive bridge network, aDC power supply for energizing said bridge, a variable impedance in onearm of said bridge, a recorder solenoid, means linked to said solenoidfor varying said impedance when said solenoid is energized until saidbridge voltage in series with the output of said electrode issubstantially equal to said predetennined voltage, and means responsiveto said calibrating means for energizing said solenoid when saidcalibrating means is actuated.

5. In an electronic apparatus for continuously monitoring the voltageoutput of a sensing electrode re resentative of the partial pressure ofa sample gas in a llqul solution having a voltage input terminal andrecorder means for responding to said voltage impressed on said inputterminal, the improvement comprising;

sample measuring timer means for breaking a contact a predeterminedsample measuring time after the cycle of said measuring timer means isinitiated, means for initiating the cycle of said sample measuring timermeans, valve control means for selectively introducing either astandardized gas or a sample gas to said electrode, means responsive tothe breaking of said contact for operating said control means toselectively introduce only said standardized gas to said electrodestandard measuring timer means responsive to the breaking of saidcontact for breaking a second contact for a second pre-det'ermined timeafter the breaking of said first contact, calibration means responsiveto the breaking of said second contact for switching the input of saidrecorder from said electrode voltage to a pre-determined voltagerepresentative of the partial pressure of the standardized gas, meansresponsive to said calibration means for generating a compensatingvoltage representative of the difference between said pre-determinedvoltage and the standardized output of said electrode, means responsiveto the breaking of said second contact for operating said valve controlmeans to selectively introduce only said sample gas to said electrodeafter a third pre-determined time after the breaking of the secondcontact means responsive to the breaking of said second contact forswitching the input of said recorder from said pre-determined voltage tosaid electrode voltage and said compensating voltage in series, andmeans responsive to the breaking of said second contact for re-cyclingsaid sample measuring timer means when said second contact is broken.

2223? I I: I OFFICE CERTIFICATE OF I CDRRECTION Patent No. 3 678 375 Dte .Iu1v18, 1972 Inventofls) Otho K. McFarland and James F. TarnburrinoIt is certified that error appears in the above-identified patent andthat said Letters Patent are hereby corrected as shown below:

IN THE C LAIMS In claim 5, line 33, delete "for" (second occurrence)and.

insert after IN THE SPECIFICATION Column 2, line 67, after the wort!"with" please insert I and Column 9, Iine I6, de1ete "94" and insert 194Column 10, line 51, delete "22" and insert 222 Signed and sealed this13th da of Merck 1973..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents

1. In an electronic apparatus for use with an ion sensing electrode, thecombination of: a readout means for recording a voltage impressedthereon having a voltage input terminal; valve control means forselectively introducing either a standard solution or a sample solutionto said electrode; standardizing means for simultaneously operating saidvalve control means to selectively introduce said standard solution tosaid electrode and impressing an output voltage from said electrode onsaid input terminal; calibrating means for automatically impressing apre-determined voltage representative of the ion concentration of thestandard solution on said input terminal, means responsive to saidcalibrating means for automatically storing a compensating voltagerepresentative of the difference between said pre-determined voltage andthe voltage generated by the sensing electrode representative of the ionconcentration of the standard solution, measuring means for selectivelyterminating said pre-determined voltage at said input terminal andautomatically impressing said compensating voltage across said inputterminal in series with an electrode voltage generated by the sensingelectrode representative of the ion concentration of a solution suchthat said compensating voltage and said electrode voltage in series aremore truly representative of the ion concentration of the solution thanis the electrode voltage alone, and means responsive to said measUringmeans for operating said valve control means to selectively introduceonly said sample solution to said electrode.
 2. In an electronicapparatus for continuously recording the voltage output of a sensingelectrode representative of the partial pressure of a gas in a liquidsolution having a voltage input terminal, movable sheet for recordingthereon, and recorder pen responsive to a voltage impressed on saidinput terminal, the improvement comprising, in combination: valvecontrol means for selectively introducing either a standardized solutionor a sample solution to said electrode; standardizing means forsimultaneously operating said valve control means to selectivelyintroduce said standard solution to said electrode and impressing anoutput voltage from said electrode on said input terminal; calibratingmeans for automatically impressing a pre-determined voltagerepresentative of the partial pressure of the gas in said standardsolution on said input terminal, means responsive to said calibratingmeans for automatically storing a compensating voltage representative ofthe difference between said pre-determined voltage and a voltagegenerated by said electrode representative of the partial pressure ofthe gas in said standard solution, measuring means for simultaneouslyterminating said pre-determined voltage at said input terminal andautomatically impressing said compensating voltage across said input inseries with a voltage generated by said electrode representative of thepartial pressure of a gas in a liquid solution such that saidcompensating voltage and said electrode voltage in series are more trulyrepresentative of the partial pressure of the gas in said liquidsolution that is the electrode voltage alone, and means responsive tosaid measuring means for operating said valve control means toselectively introduce only said sample solution to said electrode. 3.The improvement of claim 2 wherein said calibrating means forautomatically impressing said pre-determined voltage comprise a DC powersource, a fixed impedance across said power source having an adjustablevoltage divider terminal, solenoid actuated switch means for impressinga voltage divided by said voltage divider terminal across said inputterminals of said recorder, and manually operable means for energizingsaid solenoid.
 4. The improvement of claim 1 in which said means forautomatically storing said compensating voltage comprise a resistivebridge network, a DC power supply for energizing said bridge, a variableimpedance in one arm of said bridge, a recorder solenoid, means linkedto said solenoid for varying said impedance when said solenoid isenergized until said bridge voltage in series with the output of saidelectrode is substantially equal to said predetermined voltage, andmeans responsive to said calibrating means for energizing said solenoidwhen said calibrating means is actuated.
 5. In an electronic apparatusfor continuously monitoring the voltage output of a sensing electroderepresentative of the partial pressure of a sample gas in a liquidsolution having a voltage input terminal and recorder means forresponding to said voltage impressed on said input terminal, theimprovement comprising; sample measuring timer means for breaking acontact a pre-determined sample measuring time after the cycle of saidmeasuring timer means is initiated, means for initiating the cycle ofsaid sample measuring timer means, valve control means for selectivelyintroducing either a standardized gas or a sample gas to said electrode,means responsive to the breaking of said contact for operating saidcontrol means to selectively introduce only said standardized gas tosaid electrode standard measuring timer means responsive to the breakingof said contact for breaking a second contact for a secondpre-determined time after the breaking of said first contact,calibration means responsive to the breaking of said second Contact forswitching the input of said recorder from said electrode voltage to apre-determined voltage representative of the partial pressure of thestandardized gas, means responsive to said calibration means forgenerating a compensating voltage representative of the differencebetween said pre-determined voltage and the standardized output of saidelectrode, means responsive to the breaking of said second contact foroperating said valve control means to selectively introduce only saidsample gas to said electrode after a third pre-determined time after thebreaking of the second contact means responsive to the breaking of saidsecond contact for switching the input of said recorder from saidpre-determined voltage to said electrode voltage and said compensatingvoltage in series, and means responsive to the breaking of said secondcontact for re-cycling said sample measuring timer means when saidsecond contact is broken.